Essentially, for one mana they change the color of a target spell or permanent to whatever the color of the Lace may be. In theory, this is an interesting effect to bypass creatures that have protection from a given color. The fact that it can be played to bypass creatures with certain color protections is kind of interesting.
Of course, in practicality, who would want to fill a deck up with these Laces for such a situational effect? Nobody, really. That’s why they’re considered among the weakest rares, if not weakest ever, in Magic: the Gathering.
Interesting side note: there is a Lace from Time Spiral called Moonlace, which makes a target permanent colorless. Huh, you think they would’ve learned. It does have pretty art, though!